U.S. patent number 7,460,315 [Application Number 11/959,184] was granted by the patent office on 2008-12-02 for lens system.
This patent grant is currently assigned to Hon Hai Precision Industry Co., Ltd., Hong Fu Jin Precision Industry (ShenZhen) Co., Ltd.. Invention is credited to Ting-Yu Cheng, Chun-Hsiang Huang, Wen-Xiang Zhang.
United States Patent |
7,460,315 |
Cheng , et al. |
December 2, 2008 |
Lens system
Abstract
A lens system includes a positive refractive power first lens, a
negative refractive power third lens, and a negative refractive
power second lens in that order from the object side of the lens
system. Wherein the lens system satisfies the following conditions:
(1) D/TTL>1.2; (2) 4.5>R1R/R1F>2.2; and (3) f/R1F>3,
wherein, D is the diameter of a maximal image circle of the lens
system on a image plane of the lens system, TTL is a distance from
a surface of the first lens facing the object side of the lens
system to the image plane, R1R is the radius of curvature of a
surface of the first lens facing the image side of the lens system,
R1F is the radius of curvature of the surface of the first lens
facing the object side of the lens system, and f is a focal length
of the lens system.
Inventors: |
Cheng; Ting-Yu (Taipei Hsien,
TW), Zhang; Wen-Xiang (Shenzhen, CN),
Huang; Chun-Hsiang (Taipei Hsien, TW) |
Assignee: |
Hong Fu Jin Precision Industry
(ShenZhen) Co., Ltd. (Shenzhen, Guangdong Province,
CN)
Hon Hai Precision Industry Co., Ltd. (Tu-Cheng, Taipei
Hsien, TW)
|
Family
ID: |
40073806 |
Appl.
No.: |
11/959,184 |
Filed: |
December 18, 2007 |
Foreign Application Priority Data
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Aug 9, 2007 [CN] |
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2007 1 0201308 |
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Current U.S.
Class: |
359/784;
359/716 |
Current CPC
Class: |
G02B
9/12 (20130101); G02B 13/0035 (20130101) |
Current International
Class: |
G02B
9/12 (20060101); G02B 3/02 (20060101) |
Field of
Search: |
;359/708,716,784 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Choi; William C
Assistant Examiner: Dinh; Jack
Claims
What is claimed is:
1. A lens system comprising, in the order from the object side: a
positive refractive power first lens; a negative refractive power
second lens; and a negative refractive power third lens, wherein
the lens system satisfies the following conditions: D/TTL>1.2;
(1) 4.5>R1R/R1F>2.2; and (2) f/R1F>3, (3) wherein, D is
the diameter of a maximal image circle of the lens system on an
image plane of the lens system, TTL is a distance from a surface of
the first lens facing the object side of the lens system to the
image plane, R1R is the radius of curvature of a surface of the
first lens facing the image side of the lens system, R1F is the
radius of curvature of the surface of the first lens facing the
object side of the lens system, and f is a focal length of the lens
system.
2. The lens system as claimed in claim 1, wherein the following
condition is satisfied: (4)-1>R2F>R2R, wherein R2R is the
radius of curvature of a surface of the second lens facing the
image side of the lens system, and R2F is the radius of curvature
of the surface of the second lens facing the object side of the
lens system.
3. The lens system as claimed in claim 1, wherein the following
condition is satisfied: (5) 2>R3F/R3R>1, wherein R3R is the
radius of curvature of a surface of the third lens facing the image
side of the lens system, and R3F is the radius of curvature of the
surface of the third lens facing the object side of the lens
system.
4. The lens system as claimed in claim 1, wherein the Abbe constant
.nu.1 of the first lens and the Abbe constant .nu.2 of the second
lens satisfy the following conditions: (6) .nu.1>55; and (7)
.nu.2<35.
5. The lens system as claimed in claim 1, wherein the lens system
further comprises an aperture stop arranged between the first lens
and the second lens.
6. The lens system as claimed in claim 1, wherein the aperture stop
is formed directly on the surface of the first lens facing the
image side of the lens system.
7. The lens system as claimed in claim 6, wherein the aperture stop
is formed by coating a peripheral portion of the surface of the
first lens with an opaque material.
8. The lens system as claimed in claim 1, wherein the lens system
further comprises an infrared filter arranged between the third
lens and the image plane.
9. The lens system as claimed in claim 1, wherein the first lens is
a meniscus-shaped lens with a convex surface facing the object side
of the lens system.
10. The lens system as claimed in claim 1, wherein the second lens
is a meniscus-shaped lens with a convex surface facing the image
side of the lens system.
11. The lens system as claimed in claim 1, wherein the third lens
is a meniscus-shaped lens with a convex surface facing the object
side of the lens system.
12. The lens system as claimed in claim 1, wherein each of the
first lens, the second lens and the third lens is an aspheric lens.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application is related to a copending U.S. patent application
Ser. No. 11/940,905 filed Nov. 15, 2007 entitled "Lens system" with
the same assignee. The disclosure of the above-identified
application is incorporated herein by reference.
TECHNICAL FIELD
The present invention relates to a lens system and, particularly,
to a compact lens system having a small number of lens components
and a short overall length.
DESCRIPTION OF RELATED ART
Conventionally, there is a technical field of lenses where a short
overall length is demanded for use in lens modules for image
acquisition that are mounted in relatively thin equipment, such as
simple digital cameras, webcams for personal computers, and
portable imaging systems in general. In order to satisfy this
demand, previous imaging lenses have been formed using a one-piece
lens construction. Because the electronic image sensing chips
previously used with the lens modules were compact and had low
resolution, maintaining a small image size on the image sensing
chips and miniaturizing the lens systems with a small number of
lens components was a priority. In previous arrangements, even with
one-piece lens construction, aberrations were acceptable and the
incident angle of light rays onto the image sensing chip was not so
large as to be a problem.
However, in recent years, because the resolution and the size of
the image sensing chips have increased, aberrations occurring in
one-piece lenses are too large to achieve the desired optical
performance. Therefore, it has become necessary to develop a lens
system with a short overall length and with an optical performance
that matches image sensing chips having enhanced resolution and
size.
What is needed, therefore, is a lens system with a short overall
length and with relatively good optical performance.
SUMMARY
In accordance with one present embodiment, a lens system includes a
positive refractive power first lens, a negative refractive power
second lens, a negative refractive power third lens in that order
from the object side of the lens system. Wherein the lens system
satisfies the following conditions: D/TTL>1.2; (1)
4.5>R1R/R1F>2.2; and (2) f/R1F>3, (3) wherein, D is the
diameter of a maximal image circle of the lens system on a image
plane of the lens system, TTL is a distance from a surface of the
first lens facing the object side of the lens system to the image
plane, R1R is the radius of curvature of a surface of the first
lens facing the image side of the lens system, R1F is the radius of
curvature of the surface of the first lens facing the object side
of the lens system, and f is a focal length of the lens system.
BRIEF DESCRIPTION OF THE DRAWING
Many aspects of the present lens system can be better understood
with reference to the following drawings. The components in the
drawing are not necessarily drawn to scale, the emphasis instead
being placed upon clearly illustrating the principles of the
present lens system. Moreover, in the drawings, like reference
numerals designate corresponding parts throughout the several
views.
FIG. 1 is a schematic view of a lens system in accordance with an
embodiment.
FIGS. 2-4 are graphs respectively showing spherical aberration,
field curvature, and distortion for a lens system in accordance
with a first exemplary embodiment of the present invention.
FIGS. 5-7 are graphs respectively showing spherical aberration,
field curvature, and distortion for a lens system in accordance
with a second exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Embodiments will now be described in detail below, with reference
to the drawings.
Referring to FIG. 1, a lens system 100, according to an embodiment,
is shown. The lens system 100 includes a positive refractive power
first lens 10, a negative refractive power second lens 20, and a
negative refractive power third lens 30 in that order from the
object side of the lens system 100. The lens system 100 can be used
in digital cameras, mobile phones, personal computer cameras and so
on. The lens system 100 can be used for capturing images by
disposing an image sensor at an image plane 40 of the lens system
100.
In order that the lens system 100 has a short overall length and
excellent optical performance, the lens system 100 satisfies the
following conditions: D/TTL>1.2; (1) 4.5>R1R/R1F>2.2; and
(2) f/R1F>3, (3) wherein, D is the diameter of a maximal image
circle of the lens system 100 on the image plane 40, TTL is a
distance from a surface of the first lens 10 facing the object side
of the lens system 100 to the image plane 40, R1R is the radius of
curvature of a surface of the first lens 10 facing the image side
of the lens system 100, R1F is the radius of curvature of the
surface of the first lens 10 facing the object side of the lens
system 100, and f is a focal length of the lens system 100. The
first condition (1) is for limiting the overall length of the lens
system 100 by providing the relationship between the overall length
of the lens system 100 and the diameter of a maximal image circle
of the lens system on 100 on the image plane 40. The second
condition (2) is for limiting the refractive power of the first
lens 10 in order to satisfy the requirement of the refractive power
of the lens system 100. The third condition (3) is used for making
the TTL satisfy the first condition (1). In the present embodiment,
the first lens 10 is a meniscus-shaped lens with a convex surface
facing the object side of the lens system 100. Preferably, the two
surfaces of the first lens 10 are aspherical.
Preferably, the second lens 20 also satisfies the following
condition: -1>R2F>R2R, (4) wherein, R2R is the radius of
curvature of a surface of the second lens 20 facing the image side
of the lens system 100, and R2F is the radius of curvature of the
surface of the second lens 20 facing the object side of the lens
system 100. The fourth condition (4) is for limiting the refractive
power of the second lens 20 in order to correct aberrations,
especially spherical aberration, caused by the first lens 10. The
second lens 20 is a meniscus-shaped lens with a convex surface
facing the image side of the lens system 100. Preferably, the two
surfaces of the second lens 20 are aspherical.
Preferably, the third lens 30 also satisfies the following
condition: 2>R3F/R3R>1, (5) wherein, R3R is the radius of
curvature of a surface of the third lens 30 facing the image side
of the lens system 100, and R3F is the radius of curvature of the
surface of the third lens 30 facing the object side of the lens
system 100. The fifth condition (5) is for limiting the refractive
power of the third lens 30 in order to correct aberrations,
especially field curvature, caused by the first lens 10. The third
lens 30 is a meniscus-shaped lens with a convex surface facing the
object side of the lens system 100. Preferably, the two surfaces of
the third lens 30 are aspherical.
Also, in order to appropriately correct chromatic aberration of the
lens system 100, the Abbe constant .nu.1 of the first lens 10 and
the Abbe constant .nu.2 of the second lens 20 preferably satisfy
the following conditions: v1>55; and (6) v2<35. (7)
The lens system 100 further includes an aperture stop 50 and a
infrared filter 60. The aperture stop 50 is arranged between the
first lens 10 and the second lens 20 in order to reduce light flux
into the second lens 20. For further cost reduction, the aperture
stop 50 is preferably formed directly on the surface of the first
lens 10 facing the image side of the lens system 100. In practice,
a portion of the surface of the first lens 10 through which light
rays should not be transmitted is coated with an opaque material,
such as black material, which functions as the aperture stop 50.
The infrared filter 60 is arranged between the third lens 30 and
the image plane 40 for filtering infrared rays coming into the lens
system 100.
Further, the first lens 10, the second lens 20, and the third lens
30 can be made from a resin or a plastic, which makes their
manufacture relatively easy and inexpensive.
Examples of the system will be described below with reference to
FIGS. 2-7. It is to be understood that the invention is not limited
to these examples. The following are symbols used in each exemplary
embodiment.
f: focal length of the lens system 100
FNo: F number
2.omega.: field angle
R: radius of curvature
d: distance between surfaces on the optical axis of the system
Nd: refractive index of lens
.nu.: Abbe constant
In each example, both surfaces of the first lens 10, both surfaces
of the second lens 20, and both surfaces of the third lens 30 are
aspherical. The shape of each aspheric surface is provided by
expression 1 below. Expression 1 is based on a Cartesian coordinate
system, with the vertex of the surface being the origin, and the
optical axis extending from the vertex being the x-axis.
Expression 1:
.times..times..times..times. ##EQU00001## wherein, h is a height
from the optical axis to the surface, c is a vertex curvature, k is
a conic constant, and A.sub.i are i-th order correction
coefficients of the aspheric surfaces.
EXAMPLE 1
Tables 1 and 2 show lens data of Example 1.
TABLE-US-00001 TABLE 1 f = 3.52 mm FNo = 3.2 2.omega. = 68.degree.
Diameter Lens system 100 R (mm) d (mm) Nd .nu. (mm) Object infinite
1000 1.543 56.04 Object side surface of the 1.018 0.69 1.543 56.04
first lens 10 Image side surface of the 2.508 0.4 1.543 56.04 first
lens 10 Object side surface of the -1.128 0.48 1.585 29.9 second
lens 20 Image side surface of the -1.505 0.52 1.585 29.9 second
lens 20 Object side surface of the 4.18 0.75 1.543 56.04 third lens
30 Image side surface of the 2.665 0.11 1.543 56.04 third lens 30
Object side surface of the infinite 0.4 infrared filter 60 Image
side surface of the infinite 0.64 infrared filter 60 Image plane 40
infinite 4.84
TABLE-US-00002 TABLE 2 Object side Image side Object side Image
side Object side Image side surface of the surface of the surface
of the surface of the surface of the surface of the Surface first
lens 10 first lens 10 second lens 20 second lens 20 third lens 30
third lens 30 Aspherical A2 = 0.706 A2 = 3.047 A2 = 2.872 A2 =
0.915 A2 = 68.107 A2 = 25.984 coefficient A4 = 0.1063 A4 = 0.0618
A4 = 0.05480 A4 = 0.08332 A4 = 0.14744 A4 = 0.07475 A6 = 0.0721 A6
= 0.0018 A6 = 0.47247 A6 = 0.14948 A6 = 0.06216 A6 = 0.01295 A8 =
0.0793 A8 = 0.6732 A8 = 0.50517 A8 = 0.23976 A8 = 0.00413 A8 =
0.00727 A10 = 0.0321 A10 = 0.1987 A10 = 3.74357 A10 = 0.13059 A10 =
0.00694 A10 = 0.00284 A12 = 0.00107 A12 = 0.00035
FIGS. 2-4 are graphs of aberrations (spherical aberration, field
curvature, and distortion) of the lens system 100 of Example 1. In
FIG. 2, the curves c, d, and f show spherical aberration of the
lens system 100 corresponding to three types of light with
wavelength of 656.3 nm, 587.6 nm, and 435.8 nm respectively.
Generally, the spherical aberration of lens system 100 is limited
to a range from -0.04 mm to 0.04 mm, the field curvature of the
lens system 100 is limited to a range from -0.05 mm to 0.05 mm, and
the distortion of the lens system 100 is limited to a range from
-2% to 2%.
EXAMPLE 2
Tables 3 and 4 show lens data of Example 2.
TABLE-US-00003 TABLE 3 f = 3.43 mm FNo = 3.2 2.omega. =
68.4.degree. Diameter Lens system 100 R (mm) d (mm) Nd .nu. (mm)
Object infinite 1000 Object side surface of the 1.033 0.63 1.543
56.04 first lens 10 Image side surface of the 2.89 0.42 1.543 56.04
first lens 10 Object side surface of the -1.04 0.46 1.585 29.9
second lens 20 Image side surface of the -1.355 0.51 1.585 29.9
second lens 20 Object side surface of the 3.75 0.72 1.543 56.04
third lens 30 Image side surface of the 2.27 0.11 1.543 56.04 third
lens 30 Object side surface of the infinite 0.4 infrared filter 60
Image side surface of the infinite 0.635 infrared filter 60 Image
plane 40 infinite 4.71
TABLE-US-00004 TABLE 4 Object side Image side Object side Image
side Object side Image side surface of the surface of the surface
of the surface of the surface of the surface of the Surface first
lens 10 first lens 10 second lens 20 second lens 20 third lens 30
third lens 30 Aspherical A2 = 0.771 A2 = 7.297 A2 = 2.203 A2 =
0.789 A2 = 81.623 A2 = 25.962 coefficient A4 = 0.1109 A4 = 0.0452
A4 = 0.0644 A4 = 0.07905 A4 = 0.15733 A4 = 0.07717 A6 = 0.0288 A6 =
0.0196 A6 = 0.68238 A6 = 0.21234 A6 = 0.06992 A6 = 0.01388 A8 =
0.1906 A8 = 1.0076 A8 = 0.89015 A8 = 0.33342 A8 = 0.00483 A8 =
0.00854 A10 = 0.1720 A10 = 1.0933 A10 = 4.89037 A10 = 0.15324 A10 =
0.00857 A10 = 0.00348 A12 = 0.00139 A12 = 0.00045
FIGS. 5-7 are graphs of aberrations (spherical aberration, field
curvature, and distortion) of the lens system 100 of Example 1. In
FIG. 5, the curve c, d, and f show spherical aberration of the lens
system 100 corresponding to three types of light with wavelength of
656.3 nm, 587.6 nm, and 435.8 nm respectively. Generally, the
spherical aberration of lens system 100 is limited to a range from
-0.04 mm to 0.04 mm, the field curvature of the lens system 100 is
limited to a range from -0.05 mm to 0.05 mm, and the distortion of
the lens system 100 is limited to a range from -2% to 2%.
As seen in the above-described examples, the distortion of the lens
system 100 can also be limited to a range from -2% to 2% when
keeping the field angle of the lens system bigger than 60.degree..
The overall length of the lens system 100 is small, and the system
100 appropriately corrects fundamental aberrations.
While certain embodiments have been described and exemplified
above, various other embodiments will be apparent to those skilled
in the art from the foregoing disclosure. The present invention is
not limited to the particular embodiments described and exemplified
but is capable of considerable variation and modification without
departure from the scope of the appended claims.
* * * * *